# Sensor Overview
Sensors in OpenHarmony are an abstraction of underlying sensor hardware. Your application can access the underlying sensor hardware via the sensors. Using the [Sensor](../reference/apis/js-apis-sensor.md) APIs, you can query sensors on your device, subscribe to sensor data, customize algorithms based on sensor data, and develop various sensor-based applications, such as compass, motion-controlled games, and fitness and health applications.
A sensor is a device to detect events or changes in an environment and send messages about the events or changes to another device (for example, a CPU). Generally, a sensor is composed of sensitive components and conversion components. Sensors are the cornerstone of the IoT. A unified sensor management framework is required to achieve data sensing at a low latency and low power consumption, thereby keeping up with requirements of "1+8+N" products or business in the Seamless AI Life Strategy. The sensor list is as follows:
| Type | Name | Description | Usage |
| --------------------------------------- | ------------------ | ------------------------------------------------------------ | ---------------------------------------- |
| SENSOR_TYPE_ACCELEROMETER | Acceleration sensor | Measures the acceleration (including the gravity acceleration) applied to a device on three physical axes (X, Y, and Z), in the unit of m/s2.| Detecting the motion status |
| SENSOR_TYPE_ACCELEROMETER_UNCALIBRATED | Uncalibrated acceleration sensor| Measures the uncalibrated acceleration (including the gravity acceleration) applied to a device on three physical axes (X, Y, and Z), in the unit of m/s2.| Measuring the acceleration bias estimation |
| SENSOR_TYPE_LINEAR_ACCELERATION | Linear acceleration sensor | Measures the linear acceleration (excluding the gravity acceleration) applied to a device on three physical axes (X, Y, and Z), in the unit of m/s2.| Detecting the linear acceleration in each axis |
| SENSOR_TYPE_GRAVITY | Gravity sensor | Measures the gravity acceleration applied to a device on three physical axes (X, Y, and Z), in the unit of m/s2.| Measuring the gravity |
| SENSOR_TYPE_GYROSCOPE | Gyroscope sensor | Measures the rotation angular velocity of a device on three physical axes (X, Y, and Z), in the unit of rad/s.| Measuring the rotation angular velocity |
| SENSOR_TYPE_GYROSCOPE_UNCALIBRATED | Uncalibrated gyroscope sensor| Measures the uncalibrated rotation angular velocity of a device on three physical axes (X, Y, and Z), in the unit of rad/s.| Measuring the bias estimation of the rotation angular velocity |
| SENSOR_TYPE_SIGNIFICANT_MOTION | Significant motion sensor | Checks whether a device has a significant motion on three physical axes (X, Y, and Z). The value **0** means that the device does not have a significant motion, and **1** means the opposite.| Detecting significant motions of a device |
| SENSOR_TYPE_PEDOMETER_DETECTION | Pedometer detection sensor | Detects whether a user takes a step. The value can be **0** (the user does not take a step) or **1** (the user takes a step).| Detecting whether a user takes a step |
| SENSOR_TYPE_PEDOMETER | Pedometer sensor | Records the number of steps a user has walked. | Providing the number of steps a user has walked |
| SENSOR_TYPE_AMBIENT_TEMPERATURE | Ambient temperature sensor | Measures the ambient temperature, in the unit of degree Celsius (°C). | Measuring the ambient temperature |
| SENSOR_TYPE_MAGNETIC_FIELD | Magnetic field sensor | Measures the magnetic field on three physical axes (X, Y, and Z), in the unit of μT.| Creating a compass |
| SENSOR_TYPE_MAGNETIC_FIELD_UNCALIBRATED | Uncalibrated magnetic field sensor | Measures the uncalibrated magnetic field on three physical axes (X, Y, and Z), in the unit of μT.| Measuring the magnetic field bias estimation |
| SENSOR_TYPE_HUMIDITY | Humidity sensor | Measures the ambient relative humidity, in a percentage (%). | Monitoring the dew point, absolute humidity, and relative humidity |
| SENSOR_TYPE_BAROMETER | Barometer sensor | Measures the barometric pressure, in the unit of hPa or mbar. | Measuring the barometric pressure |
| SENSOR_TYPE_ORIENTATION | Orientation sensor | Measures the rotation angles of a device on three physical axes (X, Y, and Z), in the unit of rad.| Providing the three orientation angles of the screen |
| SENSOR_TYPE_ROTATION_VECTOR | Rotation vector sensor | Measures the rotation vector of a device. It is a composite sensor that generates data from the acceleration sensor, magnetic field sensor, and gyroscope sensor.| Detecting the orientation of a device in the East, North, Up (ENU) Cartesian coordinate system |
| SENSOR_TYPE_PROXIMITY | Proximity sensor | Measures the distance between a visible object and the device screen. | Measuring the distance between a person and the device during a call |
| SENSOR_TYPE_AMBIENT_LIGHT | Ambient light sensor | Measures the ambient light intensity of a device, in the unit of lux. | Automatically adjusting the screen brightness and checking whether the screen is covered on the top|
| SENSOR_TYPE_HEART_RATE | Heart rate sensor | Measures the heart rate of a user. | Providing users' heart rate data |
| SENSOR_TYPE_WEAR_DETECTION | Wear detection sensor | Checks whether a user is wearing a wearable device. | Detecting wearables |
| SENSOR_TYPE_HALL | Hall effect sensor | Detects a magnetic field around a device. | Smart cover mode of the device |
## Working Principles
The following modules work cooperatively to implement OpenHarmony sensors: Sensor API, Sensor Framework, Sensor Service, and HDF layer.
**Figure 1** How the sensor works
- Sensor API: provides APIs for performing basic operations on sensors, including querying the sensor list, subscribing to or unsubscribing from sensor data, and executing control commands. This module makes application development simpler.
- Sensor Framework: manages sensor data subscription, creates and destroys data channels, subscribes to or unsubscribes from sensor data, and implements communication with the Sensor Service module.
- Sensor Service: interacts with the HD_IDL module to receive, parse, and distribute data, manages foreground and background policies and sensors of a device, and controls sensor permissions.
- HDF layer: selects proper policies based on the hardware first in first out (FIFO) and frequency, and adapts to different devices.
## Constraints
1. To obtain data of the following sensors, you must claim the required permissions.
Table 7 Sensor data permissions
| Sensor | Permission | Sensitivity | Permission Description |
| ------------------------- | -------------------------------- | ------------ | ----------------------- |
| Acceleration sensor, uncalibrated acceleration sensor, and linear acceleration sensor| ohos.permission.ACCELEROMETER | system_grant | Allows an application to subscribe to data of these acceleration-related sensors in the motion category.|
| Gyroscope sensor and uncalibrated gyroscope sensor | ohos.permission.GYROSCOPE | system_grant | Allows an application to subscribe to data of the gyroscope-related sensors in the motion category.|
| Pedometer sensor | ohos.permission.ACTIVITY_MOTION | user_grant | Allows an application to subscribe to the motion status. |
| Heart rate sensor | ohos.permission.READ_HEALTH_DATA | user_grant | Allows an application to read health data. |
2. The APIs for subscribing to and unsubscribing from sensor data work in pairs. If you do not need sensor data, call the unsubscription API to stop sensor data reporting.